Implantable and rechargeable neural stimulator

ABSTRACT

One aspect of the present subject matter relates to an implantable medical device. An embodiment of the device comprises a rechargeable power supply adapted to be recharged through an ultrasound signal, a neural stimulator connected to the rechargeable power supply, and a controller connected to the rechargeable power supply. The neural stimulator is adapted to generate a neural stimulation signal for delivery to a neural stimulation target through an electrode. The controller is further connected to the neural stimulator to control the neural stimulator according to a neural stimulation protocol. Other aspects are provided herein.

CROSS REFERENCE TO RELATED APPLICATION

This application is a divisional of U.S. application Ser. No.11/256,907, filed Oct. 24, 2005, now issued as U.S. Pat. No. 7,616,990,which is hereby incorporated by reference in its entirety.

TECHNICAL FIELD

This application relates generally to implantable medical devices and,more particularly, to implantable and rechargeable neural stimulators.

BACKGROUND

The automatic nervous system (ANS) regulates “involuntary” organs. TheANS includes the sympathetic nervous system and the parasympatheticnervous system. The sympathetic nervous system is affiliated with stressand the “fight or flight response” to emergencies. The parasympatheticnervous system is affiliated with relaxation and the “rest and digestresponse.” The ANS maintains normal internal function and works with thesomatic nervous system. Autonomic balance reflects the relationshipbetween parasympathetic and sympathetic activity. A change in autonomicbalance is reflected in changes in heart rate, heart rhythm,contractility, remodeling, inflammation and blood pressure. Changes inautonomic balance can also be seen in other physiological changes, suchas changes in abdominal pain, appetite, stamina, emotions, personality,muscle tone, sleep, and allergies, for example.

Neural stimulation therapy has been proposed for a variety of reasons.Reduced autonomic balance (increase in sympathetic and decrease inparasympathetic cardiac tone) during heart failure has been shown to beassociated with left ventricular dysfunction and increased mortality.Research also indicates that increasing parasympathetic tone andreducing sympathetic tone may protect the myocardium from furtherremodeling and predisposition to fatal arrhythmias following myocardialinfarction. Direct stimulation of the vagal parasympathetic fibers hasbeen shown to reduce heart rate via the sympathetic nervous system. Inaddition, some research indicates that chronic stimulation of the vagusnerve may be of protective myocardial benefit following cardiac ischemicinsult. Neural stimulation also has been proposed to alleviate pain andas a therapy for hypertension.

It can be difficult to anticipate the amount of energy needed for neuralstimulation. For effective therapy, it may be necessary to stimulateneural targets intermittently or continuously. Also, high current levelsmay be effective for a larger area, or lower levels may be effective fora smaller area. A flexible power management system is needed to improveneural stimulation devices.

SUMMARY

One aspect of the present subject matter relates to an implantablemedical device. An embodiment of the device comprises a rechargeablepower supply adapted to be recharged through an ultrasound signal, aneural stimulator connected to the rechargeable power supply, and acontroller connected to the rechargeable power supply. The neuralstimulator is adapted to generate a neural stimulation signal fordelivery to a neural stimulation target through an electrode. Thecontroller is further connected to the neural stimulator to control theneural stimulator according to a neural stimulation protocol. Otheraspects are provided herein.

An embodiment of the implantable medical device comprises a structure, arechargeable battery connected to the structure, a transducer adapted tocharge the rechargeable battery using ultrasound energy, a sensorelectrically connected to the rechargeable battery, a neural stimulatorelectrically connected to the rechargeable battery, and a controllerelectrically connected to the rechargeable battery and adapted tocommunicate with the sensor and the neural stimulator. The structure isselected from a group of structures consisting of: a structure adaptedto be chronically implanted within a vessel, and a structure adapted tobe subcutaneously implanted using a hypodermic needle.

One aspect of the present subject matter relates to a system. Anembodiment of the system comprises at least two implantable medicaldevices, where each device being adapted to be chronically implantedinto a vessel. Each device includes a rechargeable battery and anultrasound transducer connected to the battery and adapted to rechargethe battery using an ultrasound signal, a neural stimulator adapted tobe powered by the battery, a sensor adapted to be powered by thebattery, a controller electrically connected to a neural stimulator andthe pressure sensor, and a communication module adapted to be powered bythe battery and to transmit and receive ultrasound communication signalsto another implantable medical device.

One aspect of the present subject matter relates to a method ofoperating an implantable medical device with a pressure sensor and aneural stimulator chronically implanted in a vessel. According to anembodiment of the method, a pressure is sensed within the vessel usingthe pressure sensor, a neural target is stimulated using the neuralstimulator, a power supply is recharged using ultrasound signals.

This Summary is an overview of some of the teachings of the presentapplication and not intended to be an exclusive or exhaustive treatmentof the present subject matter. Further details about the present subjectmatter are found in the detailed description and appended claims. Otheraspects will be apparent to persons skilled in the art upon reading andunderstanding the following detailed description and viewing thedrawings that form a part thereof, each of which are not to be taken ina limiting sense. The scope of the present invention is defined by theappended claims and their equivalents.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of one embodiment of a chronically-implanteddevice.

FIG. 2 illustrates an embodiment where the device implantedsubcutaneously using a hypodermic needle.

FIG. 3 illustrates an embodiment where a chronically-implanted device,in the form of a stent, is placed within a vessel and where the deviceincludes an encapsulated electronics platform.

FIG. 4 illustrates one embodiment of a chronically-implanted device inthe form of a stent that includes an encapsulated electronics platform.

FIG. 5 illustrates one embodiment of a chronically-implanted device inthe form of a stent that includes two encapsulated electronicsplatforms.

FIG. 6 illustrates an embodiment of a chronically-implanted devicehaving a cylindrical or radially-oriented anode and cathode.

FIG. 7 illustrates an embodiment of a chronically-implanted devicehaving a longitudinally-oriented anode and cathode.

FIG. 8 illustrates an embodiment where the chronically-implanted deviceis powered by a small rechargeable battery adapted to be recharged usingultrasound waves from an ultrasound power source.

FIG. 9 illustrates a system embodiment where two implantable neuralstimulation devices are adapted to communicate with each other.

FIG. 10 illustrates a system including an implantable medical device(IMD) and a programmer, according to various embodiments of the presentsubject matter.

FIG. 11 illustrates an embodiment where an implantable medical devicenetwork includes a planet and a plurality of satellites formed by thechronically-implanted device.

DETAILED DESCRIPTION

The following detailed description of the present subject matter refersto the accompanying drawings which show, by way of illustration,specific aspects and embodiments in which the present subject matter maybe practiced. These embodiments are described in sufficient detail toenable those skilled in the art to practice the present subject matter.Other embodiments may be utilized and structural, logical, andelectrical changes may be made without departing from the scope of thepresent subject matter. References to “an”, “one”, or “various”embodiments in this disclosure are not necessarily to the sameembodiment, and such references contemplate more than one embodiment.The following detailed description is, therefore, not to be taken in alimiting sense, and the scope is defined only by the appended claims,along with the full scope of legal equivalents to which such claims areentitled.

Embodiments of the present subject matter provide implantable andrechargeable neural stimulators. Ultrasound energy can be used torecharge the stimulators. Some embodiments integrate a stimulator and asensor in an implantable device, such that the device can autonomouslyprovide stimulation therapy based on need. For example, a neuralstimulator integrated with a pressure sensor can be activated when thesensor senses a higher blood pressure in the vasculature. The pressuresensor can use micro-electrical mechanical systems (MEMS) technology,for example. The devices can be implanted either subcutaneously or inthe vasculature depending in the sensor-stimulator pair application.Examples of integrated sensors include sensors that can sense eitherelectrical or physical physiologic parameters. These sensors can providelocalized feedback for the neural stimulation. For example, a pressuresensor can sense high blood pressure and the stimulator can stimulatethe appropriate nerve to lower the blood pressure. Such a system can beintegrated into a device with a small form factor with its own powersupply, such that the device is physically capable of being implantedthrough a hypodermic needle or intravascularly fed into a vessel, forexample. A stent-like anchoring mechanism can be used in vasculature.

Embodiments also have the ability to wirelessly communicate otherdevice(s), either inside or outside the body. Typically, such a systemcan communicate with another device within the body using ultrasound,which has minimal loss within the body. Communications with externaldevices can be performed using ultrasound, or inductive or RF telemetry.The intra-body communication allows the neural stimulation therapy to beto be coordinated with other implantable neural stimulators or otherimplantable devices such as from a cardiac rhythm management (CRM)device (e.g. pacemaker) also has such communication capability.Intrabody communication can significantly improve the efficacy of theneural stimulator, and the neural stimulation therapy.

The neural stimulator with integrated sensor can be chronicallyimplanted to treat conditions such as hypertension and chronic pain.Some device embodiments have its own power source, and some deviceembodiments are powered remotely. Diagnostic and therapy functions canbe performed at fixed times or based at least in part on feedbackreceived from the sensor.

Physiology

Neural stimulation can be used to provide therapy for a variety ofsystemic abnormalities like hypertension. Hypertension is a cause ofheart disease and other related cardiac co-morbidities. Hypertensionoccurs when blood vessels constrict. As a result, the heart works harderto maintain flow at a higher blood pressure, which can contribute toheart failure. A large segment of the general population, as well as alarge segment of patients implanted with pacemakers or defibrillators,suffer from hypertension. The long term mortality as well as the qualityof life can be improved for this population if blood pressure andhypertension can be reduced. Many patients who suffer from hypertensiondo not respond to treatment, such as treatments related to lifestylechanges and hypertension drugs. Hypertension generally relates to highblood pressure, such as a transitory or sustained elevation of systemicarterial blood pressure to a level that is likely to inducecardiovascular damage or other adverse consequences. Hypertension hasbeen arbitrarily defined as a systolic blood pressure above 140 mm Hg ora diastolic blood pressure above 90 mm Hg. Hypertension occurs whenblood vessels constrict. As a result, the heart works harder to maintainflow at a higher blood pressure. Consequences of uncontrolledhypertension include, but are not limited to, retinal vascular diseaseand stroke, left ventricular hypertrophy and failure, myocardialinfarction, dissecting aneurysm, and renovascular disease.

The automatic nervous system (ANS) regulates “involuntary” organs, whilethe contraction of voluntary (skeletal) muscles is controlled by somaticmotor nerves. Examples of involuntary organs include respiratory anddigestive organs, and also include blood vessels and the heart. Often,the ANS functions in an involuntary, reflexive manner to regulateglands, to regulate muscles in the skin, eye, stomach, intestines andbladder, and to regulate cardiac muscle and the muscle around bloodvessels, for example.

The ANS includes, but is not limited to, the sympathetic nervous systemand the parasympathetic nervous system. The sympathetic nervous systemis affiliated with stress and the “fight or flight response” toemergencies. Among other effects, the “fight or flight response”increases blood pressure and heart rate to increase skeletal muscleblood flow, and decreases digestion to provide the energy for “fightingor fleeing.” The parasympathetic nervous system is affiliated withrelaxation and the “rest and digest response” which, among othereffects, decreases blood pressure and heart rate, and increasesdigestion to conserve energy. The ANS maintains normal internal functionand works with the somatic nervous system.

The heart rate and force is increased when the sympathetic nervoussystem is stimulated, and is decreased when the sympathetic nervoussystem is inhibited (the parasympathetic nervous system is stimulated).An afferent nerve conveys impulses toward a nerve center, such as avasomotor center which relates to nerves that dilate and constrict bloodvessels to control the size of the blood vessels. An efferent nerveconveys impulses away from a nerve center.

A pressoreceptive region or field is capable of sensing changes inpressure, such as changes in blood pressure. Pressoreceptor regions arereferred to herein as baroreceptors, which generally include any sensorsof pressure changes. The baroreflex functions as a negative feedbacksystem, and relates to a reflex mechanism triggered by stimulation of abaroreceptor. Increased pressure stretches blood vessels, which in turnactivates baroreceptors in the vessel walls. Activation of baroreceptorsnaturally occurs through internal pressure and stretching of thearterial wall, causing baroreflex inhibition of sympathetic nerveactivity (SNA) and a reduction in systemic arterial pressure. Anincrease in baroreceptor activity induces a reduction of SNA, whichreduces blood pressure by decreasing peripheral vascular resistance.

Direct electrical stimulation has been applied to the vagal nerve andcarotid sinus. Research has indicated that electrical stimulation of thecarotid sinus nerve can result in reduction of experimentalhypertension, and that direct electrical stimulation to thepressoreceptive regions of the carotid sinus itself brings about reflexreduction in experimental hypertension.

Stimulating the sympathetic and parasympathetic nervous systems can haveeffects other than heart rate and blood pressure. For example,stimulating the sympathetic nervous system dilates the pupil, reducessaliva and mucus production, relaxes the bronchial muscle, reduces thesuccessive waves of involuntary contraction (peristalsis) of the stomachand the motility of the stomach, increases the conversion of glycogen toglucose by the liver, decreases urine secretion by the kidneys, andrelaxes the wall and closes the sphincter of the bladder. Stimulatingthe parasympathetic nervous system (inhibiting the sympathetic nervoussystem) constricts the pupil, increases saliva and mucus production,contracts the bronchial muscle, increases secretions and motility in thestomach and large intestine, and increases digestion in the smallintention, increases urine secretion, and contracts the wall and relaxesthe sphincter of the bladder. The functions associated with thesympathetic and parasympathetic nervous systems are many and can becomplexly integrated with each other. Thus, an indiscriminatestimulation of the sympathetic and/or parasympathetic nervous systems toachieve a desired response, such as vasodilation, in one physiologicalsystem may also result in an undesired response in other physiologicalsystems. Aspects of the present subject matter provide implantablemedical devices with a form factor (physical size and shape) adapted forminimally-intrusive implantation that allows the devices to bepositioned to specifically stimulate desired nerves.

The baroreflex is a reflex triggered by stimulation of a baroreceptor. Abaroreceptor includes any sensor of pressure changes, such as sensorynerve endings in the wall of the auricles of the heart, cardiac fatpads, vena cava, aortic arch and carotid sinus, that is sensitive tostretching of the wall resulting from increased pressure from within,and that functions as the receptor of the central reflex mechanism thattends to reduce that pressure. A baroreflex response can be induced bystimulating some afferent nerve trunks, such as the vagus, aortic andcarotid nerves, leading from the sensory nerve endings. Stimulating abaroreflex inhibits sympathetic nerve activity (stimulates theparasympathetic nervous system) and reduces systemic arterial pressureby decreasing peripheral vascular resistance and cardiac contractility.

Some aspects of the present subject matter locally stimulate specificnerve endings, such as nerve endings near or by arterial walls, ratherthan stimulate afferent nerve trunks in an effort to stimulate a desireresponse (e.g. reduced hypertension) while reducing the undesiredeffects of indiscriminate stimulation of the nervous system. Forexample, some embodiments stimulate baroreceptor sites in the pulmonaryartery. Some embodiments of the present subject matter involvestimulating either baroreceptor sites or nerve endings in the aorta, thecarotid sinus, the chambers of the heart, the fat pads of the heart, andsome embodiments of the present subject matter involve stimulating anafferent nerve trunk, such as the vagus, carotid and aortic nerves, andvarious branches of these nerves such as a cardiac branch of the vagusnerve. Some embodiments stimulate afferent nerve trunks using anintravascularly placed electrode positioned in a blood vessel proximateto the nerve, such that the electrical stimulation transvascularlypasses through the vessel wall to stimulate the nerve trunk.

Neural stimulation has been proposed to provide remodeling therapy toreverse the stiffening process caused by hypertension, and to provide atherapy for myocardial infarction to reduce or prevent myocardial damagecaused by highly stressed regions of the heart. With respect toremodeling, the slow and progressive lowering of blood pressure enablesthe slower reversion of the stiffening process through the reverseremodeling. Blood pressure is reduced without compromising cardiacoutput in the process, thus avoiding undesired patient symptoms. Withrespect to myocardial infarction therapy, it is noted that an increasedbaroreflex stimulation compensates for reduced baroreflex sensitivitythrough quick vasodilation and associated decrease in systemic bloodpressure, and improves the clinical outcome in patients following amyocardial infarction.

Neural stimulation can also be used to stimulate sensory nerves to blockpain signals from reaching the brain. The stimulation can stimulateproduction of endorphins, which are chemicals produced in the brain,often in response to stress and pain, that reduce pain perception. Inaddition to blocking neural signals to block pain, the neuralstimulation can be used to block or stimulate other neural pathways,such as to prevent or stimulate a particular muscle contraction.

Device Embodiments

FIG. 1 is a block diagram of one embodiment of a chronically-implanteddevice. According to this embodiment, the chronically-implanted device100 forms an intravascular neural stimulator and sensor that includes apower/communication circuit 102, a control circuit 104, a neuralstimulation circuit 106, and a sensing circuit 108. The components ofthe chronically-implanted device 100 will be described in more detailbelow. The neural stimulation circuit 106 functions as atherapy-providing circuit which is operative to provide the desiredtherapy, such as neural stimulation therapy to treat hypertension andneural stimulation therapy to alleviate pain. In an embodiment, thesensing circuit 108 is operative to sense pressure.

The illustrated power and communication circuitry 102 includes arechargeable battery, which is capable of being recharged usingultrasound signals. In the embodiment of FIG. 1, the power andcommunication circuitry 102 are combined into one box to illustrate thatthey are capable of being integrated. Alternatively, the power circuitryand communication circuitry are capable of being separate circuits. Withrespect to an integrated power/communication circuit, data is capable ofbeing encoded into the power transmission as a modulation of the powersignal. As such, one embodiment of the chronically-implanted device 100provides a combined power/communication link 112 between thepower/communication circuit 102 and the external device 110. Also withrespect to an integrated power/communication circuit, some embodimentsshare sub-components such as ultrasound transducer(s). Anotherembodiment of the chronically-implanted device 100 provides a power linkand a separate communication link between the power/communicationcircuit 102 and the external device 110. One embodiment of thechronically-implanted device 100 provides wireless (e.g. ultrasound),combined power/communication link. Furthermore, with respect to deviceembodiments that include separate power and communication links, thepower link is capable of being wireless (e.g. ultrasound), and thecommunication link is independently capable of being wireless (e.g.ultrasound). For example, the circuit 102 in the illustrated device caninclude a transceiver and associated circuitry for use to communicatewith a programmer or another external or internal device. Variousembodiments have wireless communication capabilities. For example, sometransceiver embodiments use a telemetry coil to wirelessly communicatewith a programmer or another external or internal device. Somecommunication modules have transducers for use to communicate throughultrasound signals.

According to one embodiment, the chronically-implanted device is anintravascular device. For example, one device embodiment has the form ofa stent or a stent-like device. Some device embodiments communicate toother implantable medical devices 114 using communication link 116. Someembodiments use an ultrasound communication link 116. According tovarious embodiments, the device functions as a satellite andcommunicates to a planet by way of ultrasound energy.

According to one embodiment, the chronically-implanted device includescontrol circuitry 104 to control the functions of one or more of thesubsystems or components shown in FIG. 1. According to variousembodiments, the chronically-implanted device employs a dedicatedcontroller to monitor, to control, or to monitor and control thefunctions of any or all of the components. According to variousembodiments, the controller is adapted to trigger the sensing circuit,the stimulating circuit, or the sensing and stimulating circuits.According to one embodiment, the controller is used to manage systempower by controlling power flow between the power circuitry and othersystem components. The controller is capable of controlling theoperation of any system component, and of providing the system clock forelectronics timing and functionality. According to one embodiment, thecontroller is a state machine. The illustrated device includescontroller circuitry 104 and a memory 118. The controller circuitry iscapable of being implemented using hardware, software, and combinationsof hardware and software. For example, according to various embodiments,the controller circuitry includes a processor to perform instructionsembedded in the memory to perform functions associated with NS therapysuch as AHT therapy. The illustrated IMD is adapted to perform neuralstimulation functions. Some embodiments of the illustrated IMD performsan anti-hypertension (AHT) function.

The illustrated device further includes neural stimulation circuitry106. Various embodiments of the device also includes sensor circuitry108. The neural stimulation circuitry is used to apply electricalstimulation pulses to desired neural target sites, such as baroreceptorsites in the pulmonary artery, through one or more stimulationelectrodes. In various embodiments, at least one electrode is connectedto the neural stimulation circuitry using a lead such that the neuralstimulation circuitry applies electrical stimulation through the leadand electrode. In various embodiments, at least one electrode iswirelessly coupled to the neural stimulation circuitry such that theneural stimulation circuitry wirelessly applies electrical stimulationto the electrode. Such wireless embodiments provide additionalflexibility in placement of the electrode(s) and device. In variousembodiments, at least one electrode is integrated with or otherwiseformed on the housing of the device such that the neural stimulationcircuitry applies electrical stimulation through the electrode on thehousing. The sensor circuitry can be used to provide feedback for theneural stimulation. For example, the sensing circuit 108 can be used todetect and process ANS nerve activity and/or surrogate parameters suchas blood pressure, respiration and the like, to determine the ANSactivity.

According to various embodiments, the stimulator circuitry 106 includesmodules to set any one or any combination of two or more of thefollowing pulse features: the amplitude of the stimulation pulse, thefrequency of the stimulation pulse, the burst frequency or duty cycle ofthe pulse, and the wave morphology of the pulse. Examples of wavemorphology include a square wave, triangle wave, sinusoidal wave, andwaves with desired harmonic components to mimic white noise such as isindicative of naturally-occurring baroreflex stimulation.

Various implantable neural stimulator embodiments include an integratedpressure sensor (IPS), to monitor changes in blood pressure, forexample. Thus, the sensor monitors the effect of the neural stimulation.In various embodiments, for example, micro-electrical mechanical systems(MEMS) technology is used to sense the blood pressure. Some sensorembodiments determine blood pressure based on a displacement of amembrane. The stimulator and sensor functions can be integrated, even ifthe stimulator and sensors are located in separate devices.

This device, for example, is capable of being intravascularly introducedor subcutaneously introduced by a hypodermic needle to stimulate aneural target, such as the baroreceptor sites in the pulmonary artery,the aortic arch, the ligamentum arteriosum, the coronary sinus, and theatrial and ventricular chambers, and neural targets such as the cardiacfat pads.

Thus, various embodiments of the present subject matter provide animplantable neural stimulation device that automatically modulatesneural stimulation using an IPS based, at least in part, on localizedfeedback from the integrated pressure sensor. This localized sensingimproves feedback control. According to various embodiments, the devicemonitors pressure parameters such as mean arterial pressure, systolicpressure, diastolic pressure and the like. As mean arterial pressureincreases or remains above a programmable target pressure, for example,the device stimulates the baroreflex at an increased rate to reduceblood pressure and control hypertension. As mean arterial pressuredecreases towards the target pressure, the device responds by reducingthe stimulation of the baroreflex. In various embodiments, the algorithmtakes into account the current metabolic state (cardiac demand) andadjusts neural stimulation accordingly. A neural stimulation devicehaving an IPS is able to automatically modulate neural stimulation,which allows an implantable NS device to determine the level ofhypertension in the patient and respond by delivering the appropriatelevel of therapy.

An aspect of the present subject matter relates to achronically-implanted stimulation device specially designed to treathypertension by monitoring blood pressure and stimulating baroreceptorsto activate the baroreflex and inhibit sympathetic discharge from thevasomotor center. Baroreceptors are located in various anatomicallocations such as the carotid sinus and the aortic arch. Otherbaroreceptor locations include the pulmonary artery, including theligamentum arteriosum, and sites in the atrial and ventricular chambers.In various embodiments, the neural stimulation device is integrated intoa pacemaker/defibrillator or other electrical stimulator system.Components of the system include a pulse generator, sensors to monitorblood pressure or other pertinent physiological parameters, electrodesto apply electrical stimulation to neural targets, algorithms operatedon by a controller to determine the when and how to administerstimulation, and algorithms operated on by the controller to manipulatedata for display and patient management. The controller is adapted tocontrol the neural stimulator to provide a neural stimulation therapyusing feedback from the pressure sensor. According to variousembodiments, the therapy includes one or more of a treatment followingmyocardial infarction, a treatment to alleviate pain, and a therapy forhypertension. As those of ordinary skill in the art will understand uponreading and comprehending this disclosure, other neural stimulationtherapies can be performed.

A system according to these embodiments can be used to augment partiallysuccessful treatment strategies. As an example, undesired side effectsmay limit the use of some pharmaceutical agents. The combination of asystem according to these embodiments with reduced drug doses may beparticularly beneficial.

Form Factor (Size/Shape)

According to one embodiment, the electrical stimulation functionsprovided by the intravascular device involves only a minimally invasivesurgery, even when several electrodes are placed for multisite pacing.Strategies that incorporate multisite pacing are believed to offertherapeutic advantages.

FIG. 2 illustrates the device 200 implanted subcutaneously using ahypodermic needle 220. One embodiment of the chronically-implanteddevice is an intravascular device. One intravascular device embodimenthas a structure of a stent for preventing restenosis. For example, inthe embodiment in which the chronically-implanted device has astent-like form, the structure of the expanded device exerts a pressureon vascular walls to prevent restenosis. Additionally, variousembodiments of the chronically-implanted device includes appropriatesensors for monitoring mechanical/fluid properties such as thehemodynamic properties of blood flow and pressure. The sensing functionis described in more detail below. Embodiments of the stent-like,chronically-implanted device include balloon-expandable stents andself-expanding stents. The expanded stent applies pressure against theinterior of the vessel to widen the vessel. The catheter is removed,leaving the expanded stent securely in place. Furthermore, oneembodiment of the chronically-implanted device has the structure of andperforms the mechanical function of a vascular occlusion device.

FIG. 3 illustrates a chronically-implanted device 300 in the form of astent placed within a vessel 322 in which the device includes anencapsulated electronics platform. Intelligent functions, in addition tothe mechanical function of preventing restenosis, are capable of beingperformed by the stent because of circuitry, or microsystems, containedon the electronics platform.

The chronically-implanted device diminishes problems associated withinvasive surgical procedures because the device is small and is capableof being placed by a hypodermic needle or a catheter, for example, intoposition through the vascular network or through the lumen of othercanals or tubular structures of a biosystem.

According to various embodiments, the chronically-implanted device ofthe present subject matter may be formed to function as a variety ofstents. These stents include, but are not limited to, a coronary stent,a vascular stent, a tracheobronchial stent, a colonic/duodenal stent, anesophageal stent, a biliary stent, a urological stent, a neurovascularstent, an abdominal aortic aneurysm stent, a renal stent, and a carotidstent.

FIG. 4 illustrates one embodiment of a chronically-implanted device 400in the form of a stent that includes an encapsulated electronicsplatform 424. The electronics platform 424 includes the circuitry fromthe various embodiments previously shown and described with respect toFIG. 1. FIG. 5 illustrates one embodiment of a chronically-implanteddevice 500 in the form of a stent that includes two encapsulatedelectronics platforms 524. Additional electronic platforms may beincorporated as desired. One embodiment of the device includes at leastone dedicated electrical connector that couples two or more electronicsplatforms. One embodiment of the device uses an insulated strand of mesh526 from the stent structure to couple two or more electronicsplatforms.

The stent-like structure of one embodiment of a chronically-implanteddevice includes at least two conducting portions separated by aninsulator. One of the conducting portions functions as an anode andanother functions as a cathode. These conducting portions are used,according to various embodiments of the chronically-implanted device, toprovide electrical therapy (e.g. neural stimulation), to receive powertransmissions, and/or to receive and transmit communicationtransmissions.

FIG. 6 illustrates one embodiment of a chronically-implanted device 600having a cylindrical or radially-oriented anode 628 and cathode 630.FIG. 7 illustrates one embodiment of a chronically-implanted device 700having a longitudinally-oriented anode 728 and cathode 730. According tovarious embodiments, these split stent-like structures are formed from aconventional stent. The conventional stent is cut as required to form orisolate a radially-oriented anode and cathode or alongitudinally-oriented anode and cathode. The anode and cathode arerecombined using an insulator material 632 or 732.

Rechargeable Power Supply

The chronically-implanted device includes power circuitry. According tovarious embodiments, for example, the power circuitry forms part of thepower/communication circuit 102 of FIG. 1. As illustrated in FIG. 8,some embodiments of the chronically-implanted device is powered by asmall rechargeable battery adapted to be recharged using ultrasoundwaves 836 from an ultrasound power source 838. The use of ultrasoundallows the device to be recharged remotely. The illustrated device 800includes an ultrasound transducer 840, or an array of transducers, toconvert the ultrasound signals into an electrical signal. Examples ofultrasonic transducers include an acoustic, piezoelectric,electrostatic, and magnetostrictive devices. Recharging circuitry 842 isconnected to receive the electrical signal from the transducer andprocess the signal to charge to battery 834.

Communication

The chronically-implanted device includes communication circuitry usedto communicate to an external device. According to various embodiments,for example, the communication circuitry forms part of thepower/communication circuits 102 of FIG. 1. Embodiments providecommunication between the chronically-implanted device and the externaldevice using ultrasound waves, for example. As illustrated in FIG. 9,two implantable neural stimulation devices 900A and 900B are adapted tocommunicate with each other. Each device has communication circuitry 944with an ultrasound transducer 946 for receiving and generating anultrasound signal. The communication circuitry is adapted to process thesignals into information understandable by the device.

Neural Stimulator

According to one embodiment, the neural stimulator has adjustablestimulation parameters such as pulse width, frequency, duty cycle, burstduration, amplitude, stimulation modes (bi-polar or uni-polar, forexample), and stimulation site if multiple sites are available.According to one embodiment, the neural stimulation circuitry receivesits parameters from the controller.

The device includes electrode(s) to provide neural stimulation. Somedevice embodiments sense electrical signals with electrode(s). Someelectrode embodiments are connected to the device by a lead or tether.In some embodiments, the electrode is attached to the device housing;and in some embodiments, the electrode forms at least part of the devicehousing.

Electrode embodiments include intravascularly-placed electrodes andelectrodes placed subcutaneously. With respect to intravascularly-placedembodiments, at least one an electrode is placed in a blood vessel andpositioned to transvascularly stimulate a nerve on or near theextravascular surface of the vessel. Transvascular stimulation avoidsdirect contact with nerves during stimulation and reduces problemsassociated with neural inflammation or injury induced by directstimulation. Transvascular stimulation using intravascularly-fed leadsprovides relatively non-invasive access to anatomical targets and pointsof innervation.

In an example, the expandable electrode includes a mesh, at least partof which is electrically conductive. In an example, the expandableelectrode is formed from Platinum or Platinum-Iridium. In an embodiment,the expandable electrode is similar to a stent. A nerve trunk extends onor near an extravascular surface of the blood vessel. An expandableelectrode can be implanted at or near a location in the blood vesselwhere the nerve trunk crosses the blood vessel. In an example, theexpandable electrode transmits neural stimulation energy through apredetermined surface area of the wall of a blood vessel. In an example,the expandable electrode has a length that provides enough surface areathat there is at least some flexibility in the placement of theexpandable electrode in the vessel with respect to the target nerve. Inan example, the length of the expandable electrode is about 0.5 to 2.0cm.

In an embodiment, the entire surface area of the expandable electrodethat touches the blood vessel wall is conductive. In an embodiment, atleast a part of the surface area of the electrode is non-conductive. Forexample, an electrode can be formed and positioned to deliverstimulation to through a conductive part of the electrode to a portionof a blood vessel that is proximate a nerve. The expandable electrodehas an expanded diameter that is sized for implantation in a bloodvessel of a particular size range. In one example, where the electrodeis size for implantation in the internal jugular vein, the expandeddiameter is about 0.5 to 1.5 cm, and the length of the electrode isabout 1.0 cm.

In an example, the expandable electrode is covered with a drug, such asa drug that prevents occlusion, or a drug that reduces inflammation ofthe blood vessel near the electrode. The expandable electrode is coupledto a power source that delivers an electrical stimulation. The electrodecan be coupled to the power source through a lead, or the electrode canform at least part of a device structure that contains the power source.

The electrode(s) may be implanted in various locations in the body,including a variety of locations near a trunk or branch of a sympatheticor parasympathetic nerve system. In an example, the electrodetransvascularly stimulates a peripheral nerve trunk. Examples of aperipheral nerve trunk include the vagus nerve, aortic nerve, andcarotid sinus nerve. In another example, the electrode stimulates anerve branch, such as a vagal cardiac branch. The electrode(s) can beimplanted in various vessels or chambers such as the superior vena cava(SVC) to transvascularly stimulate a nerve or nerve trunk on or near theSVC, and a coronary sinus.

Electrodes can be implanted within the atria, the ventricle, superiorvena cava, inferior vena cava, aorta, right pulmonary veins, and rightpulmonary artery, and coronary sinus. An electrode can be implanted inone or more of the blood vessels listed above at a location where anerve, nerve branch, or nerve trunk passes an extravascular surface ofthe blood vessel. The implanted electrode transvascularly stimulates anerve, nerve branch, or nerve trunk through the blood vessel. In oneexample, an electrode is implanted in the SVC near a vagal nerve trunk.In another example, an electrode is implanted in the coronary sinus neara vagal nerve trunk.

In another example, a cardiac fat pad is transvascularly stimulated byan implanted electrode. A cardiac fat pad is located between thesuperior vena cava and aorta, a cardiac fat pad is located proximate tothe right cardiac veins, and a cardiac fat pad is located proximate tothe inferior vena cava and left atrium. Electrodes implanted in thesuperior vena cava, aorta, cardiac veins, inferior vena cava or coronarysinus can be used to stimulate various cardiac fat pads.

Electrodes can be implanted at locations in blood vessels near a vagusnerve. The right vagus nerve trunk extends near the carotid artery andsubclavian artery. The left vagus nerve extends near the carotid arteryand subclavian artery. Additionally, electrodes can be implanted in thecarotid sinus near the carotid sinus nerve.

The left vagus nerve extends next to a subclavian artery also extendspast the ligamentum arteriosum. Various nerves extend around the arch ofthe aorta. The anterior pulmonary plexus crosses the left pulmonaryartery. The right vagus nerve extends past a subclavian artery and thecupola of pleura. Cardiac nerves extend past the brachiocephalic trunknear the trachea. Cardiac nerves also extend past the arch of an azygosvein to the right pulmonary artery. A left phrenic nerve extends past acupola of pleura, an internal thoracic artery, and left pulmonaryartery. The vagus nerve, recurrent laryngeal nerves, cardiac nerves, andthe anterior pulmonary plexus extend near the left pulmonary artery andligamentum arteriosum. An expandable electrode, such as a stent, ischronically implantable in these blood vessels to transvascularlystimulate a nerve or nerve trunk that extends on or near these bloodvessel. For example, the vagus nerve can be transvascularly stimulatedfrom the azygos vein or internal jugular vein. An afferent nerve conveysimpulses toward a nerve center, and an efferent nerve conveys impulsesaway from a nerve center. Both afferent and efferent nerves can bestimulated transvascularly. In other examples, nerve trunks innervatingother organs, such as the lungs or kidneys are transvascularlystimulated.

Sensor(s)

According to one embodiment, the sensor functions provided by the deviceare capable of providing continuous intravascular measurements, such asblood pressure, blood flow and vessel size. According to one embodiment,the chronically-implanted device, or system of devices, communicateswith a central unit, such as an implantable device, and monitors bloodflow, blood pressure, and vessel inner diameter.

According to various embodiments, Micro-Electro-Mechanical Systems(MEMS) technology is used to fabricate the required circuitry for thechronically-implanted device on silicon substrate. Currently, forexample, the MEMS circuitry is between about 1 mm×3 mm for some of thepresent applications; however, the MEMS circuitry is capable of beingotherwise sized. MEMS devices have been used in catheter-based systemsto measure intracardiac pressure and temperature.

In general, a MEMS device contains micro-circuitry on a tiny siliconchip into which some mechanical device such as a sensor has beenmanufactured. These chips are able to be built in large quantities atlow cost, making the MEMS device cost-effective. MEMS technologyintegrates mechanical elements, sensors, actuators, and electronics on acommon silicon substrate using microfabrication technology. MEMScombines silicon-based microelectronics with microsensors andmicroactuators to provide a complete system on a chip. Themicromechanical components are fabricated using micromachining processesthat are compatible with the integrated circuit process sequences. Partsof the silicon wafer are selectively etched away or new structurallayers are added to form the mechanical and electromechanical devices.According to various embodiments of the chronically-implanted device, atleast one of the components (i.e. the power circuitry, the communicationcircuitry, the control circuitry, the stimulation circuitry, and thesensing circuitry) are integrated onto silicon MEMS technology to reducesize.

Examples of pressure sensors include capacitive membrane andpiezoelectric sensors. According to various embodiments, the capacitivemembrane sensor is used to measure pressure within the vessel wall, toderive flow, to derive rate, to monitor cardiac output, to monitorhemodynamic stability, and to monitor Electro-Mechanical Dissociation(EMD). It was stated earlier in the background that there is acorrelation between cardiac electrical abnormalities and coronaryvascular abnormalities. However, it is possible that the electricalfunctions appear normal but the mechanical functions are abnormal, orthat the mechanical functions are normal but the electrical functionsappear abnormal. EMD identifies conditions in which electrical andmechanical functions of the biological system are not in accord oragreement with each other.

According to various embodiments, the piezoresistive sensor is used tomeasure pressure within the vessel wall, to derive flow, to derive rate,to monitor cardiac output, to monitor hemodynamic stability, and tomonitor EMD. In one embodiment the piezoresistive sensor is used tomeasure contraction strength of the heart.

System Embodiments

FIG. 10 illustrates a system 1050 including an implantable medicaldevice (IMD) 1052 and a programmer 1054, according to variousembodiments of the present subject matter. Various embodiments of theIMD 1052 include neural stimulator functions only, and variousembodiments include a combination of NS and CRM functions. Theprogrammer 1054 and the IMD 1052 are capable of wirelessly communicatingdata and instructions. In various embodiments, for example, theprogrammer and IMD use telemetry coils to wirelessly communicate dataand instructions. Some embodiments use ultrasound transducers forcommunications, and some embodiments use ultrasound transducers torecharge the IMD. Thus, the programmer can be used to adjust theprogrammed therapy provided by the IMD, and the IMD can report devicedata (such as battery data and lead resistance) and therapy data (suchas sense and stimulation data) to the programmer using radio telemetry,for example. According to various embodiments, the IMD stimulatesbaroreceptors to provide NS therapy such as AHT therapy. Variousembodiments of the IMD stimulate neural targets using a lead fed throughvasculature. Various embodiments of the IMD have a form factor conduciveto subcutaneous implantation through a hypodermic needle. According tovarious embodiments, the IMD includes a sensor to sense ANS activity.Such a sensor can be used to perform feedback in a closed loop controlsystem. For example, various embodiments sense surrogate parameters,such as respiration and blood pressure, indicative of ANS activity.Thus, various embodiments provide a pressure sensor to sense pressure.According to various embodiments, the IMD further includes cardiacstimulation capabilities, such as pacing and defibrillating capabilitiesin addition to the capabilities to stimulate baroreceptors and/or senseANS activity.

According to one embodiment, the chronically-implanted device isincorporated as one or more satellites in a satellite-planetconfiguration. FIG. 11 illustrates an implantable medical device networkincluding a planet 1160 and a plurality of satellites 1162 formed by thechronically-implanted device. The planet 1160 can be either anotherimplantable device (e.g. cardiac rhythm management device) or anexternal device (e.g. programmer). The satellites are capable of beingplaced throughout a biosystem according the desired application.

In general, the planet is implanted or externally retained. The planetis capable of wirelessly communicating, i.e. without a direct electricalconnection, to each satellite using ultrasound, for example, or iscapable of being tethered to each satellite. The planet individuallycommands each satellite to provide sensing functions and therapyfunctions such as delivering electrical pulses or drugs. In anotherembodiment, the satellites function autonomously and are incommunication with the planet. This communication is initiated by theplanet and/or by the satellite in various embodiments. Additionally,each satellite is capable of determining when a sense event hasoccurred, along with an identifying code indicating to the planet whichsatellite detected the sense event. In one embodiment, the planetprocesses the encoded signals received from the network of satellites,assigns time values to each satellite when that satellite detects asense event, compares the time values to a template of normal timevalues, and determines if a therapy should be applied. Further, theplanet selects and applies the appropriate therapy for the sensed event.In various embodiments, the satellites are self-powered using arechargeable battery capable of being recharged using ultrasound.

Therapy Examples

According to various embodiments, the therapy includes one or more of atreatment following myocardial infarction, a treatment to alleviatepain, and a therapy for hypertension.

Neural stimulation therapies can be used to treat one or more of avariety of conditions, including but not limited to arrhythmias, heartfailure, syncope, or orthostatic intolerance. In an example, an efferentperipheral nerve is transvascularly stimulated by an implantedexpandable electrode. In another example, an afferent peripheral nerveis stimulated.

In an example, electrical stimulation is transvascularly delivered to aparasympathetic nerve to reduce chronotropic, ionotropic, anddromotropic responses in the heart. In a therapy example, electricalstimulation is transvascularly delivered to a parasympathetic nervetrunk during heart failure. In another therapy example, electricalstimulation is transvascularly delivered to a parasympathetic nervetrunk following a myocardial infarction to protect against arrhythmiasor prevent cardiac remodeling.

Transvascular stimulation of a vagus nerve trunk is used in a number oftherapies. In an example, vagal nerve stimulation simultaneouslyincreases parasympathetic tone and decreases sympathetic myocardialtone. In an example, a vagus nerve trunk is transvascularly stimulatedfollowing cardiac ischemic insult. Increased sympathetic nervousactivity following ischemia often results in increased exposure of themyocardium to epinephrine and norepinephrine. These catecholaminesactivate intracellular pathways within the myocytes, which lead tomyocardial death and fibrosis. This effect is inhibited by stimulationof the parasympathetic nerves, such as vagus nerves. In an example,vagal stimulation from the SVC lowers heart rate, overall bloodpressure, and left ventricular pressure. Stimulation of the vagalcardiac nerves following myocardial infarction, or in heart failurepatients, can be beneficial in preventing further remodeling andarrhythmogenesis.

In other examples, transvascular neural stimulation is used to treatother conditions such as hypertrophic cardiomyopathy (HCM) or neurogenichypertension, where an increase parasympathetic cardiac tone andreduction in sympathetic cardiac tone is desired. In another example, abradycardia condition is treated by transvascularly stimulating asympathetic nerve trunk. In another example, the ionotropic state of theheart is increased by transvascularly stimulating a sympathetic nervetrunk.

Another example of a neural stimulation therapy includes FunctionalElectric Stimulation (FES), such as may be used in a therapy for footdrop, standing, walking, hand grasp, and shoulder control. FES can beused as a therapy for spinal cord injuries, and its debilitating effecton a variety of bodily functions. In various embodiments, electrodesused in FES therapies can be subcutaneously placed near or next to adesired nerve for the therapy. Other examples include therapies for thetreatment of stroke, epilepsy, eating disorders, sleeping disorders, andpain. Various facial nerves can be stimulated to treat facial droop,migraine headaches and other headaches, for example. These therapyexamples are not intended to be exclusive, as those of ordinary skill inthe art will understand, upon reading and understanding this disclosure,how to apply the present subject matter for other neural stimulationtherapies.

This disclosure includes several processes, circuit diagrams, andstructures. The present invention is not limited to a particular processorder or logical arrangement. Although specific embodiments have beenillustrated and described herein, it will be appreciated by those ofordinary skill in the art that any arrangement which is calculated toachieve the same purpose may be substituted for the specific embodimentsshown. This application is intended to cover adaptations or variations.It is to be understood that the above description is intended to beillustrative, and not restrictive. Combinations of the aboveembodiments, and other embodiments, will be apparent to those of skillin the art upon reviewing the above description. The scope of thepresent invention should be determined with reference to the appendedclaims, along with the full scope of equivalents to which such claimsare entitled.

What is claimed is:
 1. A method of operating an implantable medicaldevice chronically implanted in a vessel wherein the device includes apressure sensor, a neural stimulator and a power supply, the methodcomprising: sensing a pressure within the vessel using the pressuresensor; stimulating a neural target using the neural stimulator; andrecharging the power supply using ultrasound signals.
 2. The method ofclaim 1, further comprising communicating with another device usingultrasound signals.
 3. The method of claim 2, wherein communicating withanother device using ultrasound signals includes communicating withanother implantable device using ultrasound signals.
 4. The method ofclaim 2, wherein communicating with another device using ultrasoundsignals includes using shared subcomponents for a communication moduleto communicate using ultrasound signals and a power module to rechargethe power supply using ultrasound signals.
 5. The method of claim 1,wherein stimulating the neural target using the neural stimulatorincludes stimulating the neural target using an electrode on a housingof the implantable device.
 6. The method of claim 1, wherein stimulatingthe neural target includes transvascularly stimulating the neural targetoutside of the vessel using an electrode in the vessel.
 7. The method ofclaim 1, further comprising enabling the neural stimulator to stimulatethe neural target in response to a sensed pressure within the vessel. 8.The method of claim 1, wherein the neural target includes an afferentnerve trunk, the method further comprising delivering a baroreflextherapy, wherein delivering the baroreflex therapy includes:transvascularly stimulating the afferent nerve trunk to trigger abaroreflex response; and controlling the stimulation of the afferentnerve trunk using sensed pressure as feedback.
 9. The method of claim 1,wherein the neural target includes baroreceptors, the method furthercomprising delivering a baroreflex therapy, wherein delivering thebaroreflex therapy includes: stimulating the baroreceptors to trigger abaroreflex response; and controlling the stimulation of thebaroreceptors using sensed pressure as feedback.
 10. The method of claim1, wherein stimulating the neural target includes eliciting aparasympathetic or sympathetic response.
 11. The method of claim 10,further comprising delivering a hypertension therapy, wherein deliveringthe hypertension therapy includes reducing pressure in the vessel. 12.The method of claim 10, further comprising delivering a remodelingtherapy, wherein delivering the remodeling therapy includes stimulatingthe neural target.
 13. The method of claim 1, further comprisingdelivering a therapy to alleviate pain, wherein delivering the therapyto alleviate pain includes stimulating the neural target to block painsignals.
 14. The method of claim 1, further comprising controlling amuscle, wherein controlling the muscle includes stimulating the neuraltarget to contract or relax the muscle.
 15. The method of claim 1,wherein stimulating the neural target includes stimulating a cardiacnerve.
 16. The method of claim 1, wherein stimulating the neural targetincludes stimulating a vagus nerve.
 17. The method of claim 1, whereinstimulating the neural target includes delivering a neural stimulationsignal through a lead to an electrode in the vessel to stimulate theneural target.
 18. The method of claim 1, wherein stimulating the neuraltarget includes wirelessly delivering a neural stimulation signal to anelectrode in the vessel to stimulate the neural target.
 19. A method,comprising: chronically implanting an implantable medical device in avessel wherein the device includes a pressure sensor, a neuralstimulator and a power supply; sensing a pressure within the vesselusing the pressure sensor; stimulating a neural target using the neuralstimulator; and recharging the power supply using ultrasound signals.20. The method of claim 19, wherein chronically implanting theimplantable medical device includes expanding a structure to secure thedevice within the vessel.